Scientists have in a study drawn attention to the previously under-appreciated risks to marine animals from crude oil exposure, and said oil spills can cause cardiac arrest and sudden death of dolphins, turtles and tunas.
Crude oil interferes with fish heart cells. The toxic consequence is a slowed heart rate, reduced cardiac contractility and irregular heartbeats that can lead to cardiac arrest and sudden cardiac death, Scientists from Stanford University and the National Oceanic and Atmospheric Administration (NOAA) have discovered.
The research, published in the Feb 14 issue of Science, is part of the ongoing Natural Resource Damage Assessment of the April 2010 Deepwater Horizon oil spill.
While crude oil is known to be cardio-toxic to developing fish, the physiological mechanisms underlying its harmful effects were unclear.
Stanford and NOAA scientists studying the impact of crude oil from the Deepwater Horizon spill on tuna discovered that it interrupts the ability of fish heart cells to beat effectively.
Crude oil is a complex mixture of chemicals, some of which are known to be toxic to marine animals.
Past research has focused in particular on "polycyclic aromatic hydrocarbons" (PAHs), which can also be found in coal tar, creosote, air pollution and stormwater runoff from land.
In the aftermath of an oil spill, PAHs can persist for many years in marine habitats and cause a variety of adverse environmental effects.
The researchers report that oil interferes with cardiac cell excitability, contraction and relaxation -- vital processes for normal beat-to-beat contraction and pacing of the heart.
Their tests revealed that very low concentrations of crude oil disrupt the specialized ion channel pores -- where molecules flow in and out of the heart cells -- that control heart rate and contraction in the cardiac muscle cell.
This cyclical signalling pathway in cells throughout the heart is what propels blood out of the pump on every beat. The protein components of the signalling pathway are highly conserved in the hearts of most animals, including humans.
The researchers found that oil blocks the potassium channels distributed in heart cell membranes, increasing the time to restart the heart on every beat. This prolongs the normal cardiac action potential, and ultimately slows the heartbeat, reports Science Daily.
The potassium ion channel impacted in the tuna is responsible for restarting the heart muscle cell contraction cycle after every beat, and is highly conserved throughout vertebrates, raising the possibility that animals as diverse as tuna, turtles and dolphins might be affected similarly by crude oil exposure.
"The ability of a heart cell to beat," explained Barbara Block, a professor of marine sciences at Stanford, "depends on its capacity to move essential ions like potassium and calcium into and out of the cells quickly. This dynamic process, which is common to all vertebrates, is called 'excitation-contraction coupling.' We have discovered that crude oil interferes with this vital signalling process essential for our heart cells to function properly."